The present disclosure relates to a diaphragm unit, i.e., a so-called iris diaphragm. The present disclosure further relates a lens apparatus including the diaphragm unit, and an image pickup apparatus including the diaphragm unit.
A diaphragm unit, i.e., a so-called iris diaphragm, is widely known (for example, see Japanese Patent Application Laid-open No. H02-156233 and Japanese Patent No. 4954605 (hereinafter referred to as Patent Documents 1 and 2)).
In the full-aperture, the depth of field is small (i.e., focus-adjustable range is narrow). Near the full-aperture, the shape of an aperture of a diaphragm unit affects the appearance quality of a taken image. Specifically, the shape of the aperture affects the shape of blurring and a ghost.
Further, in the middle-aperture to the small-aperture, the depth of field is large (i.e., focus-adjustable range is wide). Near the middle-aperture to the small-aperture, the shape of an aperture of a diaphragm unit affects the appearance quality of a taken image. Specifically, the shape of the aperture affects the shape of blurring and a ghost. In addition, the circle-radius-ratio is decreased. As a result, a portion, in which blades overlap with each other, is acute-angled. Then, light is diffracted at that portion. As a result, the resolving power is degraded, and flare/stray light occur. As a result, the appearance quality of a taken image is degraded.
In view of this, it is desirable that the shape of an aperture be nearly circular. That is, it is desirable that the circle-radius-ratio be higher. Note that the circle-radius-ratio means the ratio (R1/R2) between the radius (R1) of an inscribed circle of an aperture and the radius (R2) of a circumscribed circle of the aperture.
The shape of an aperture of a diaphragm unit is determined based on the shape of the inner periphery of a diaphragm blade. The inner periphery means a periphery of the diaphragm blade, which forms the outer periphery of the aperture.
In general, the shape of the inner periphery is designed by combining a plurality of Rs (radii).
Each of the above-mentioned Patent Documents 1 and 2 discloses the following diaphragm unit. That is, a plurality of arcs are connected smoothly, whereby the shape of an inner periphery of a diaphragm blade is formed. The distance between the origin of each arc and the rotary shaft of the diaphragm blade is uniform. That is, the origins of all the arcs are on one arc. The origin of the one arc is the rotary shaft of the diaphragm blade. The radius of the one arc is the same as the distance between the rotary shaft and the origin of the aperture.